The presently available equipment for making wrapped strings is basically quite old and has not changed materially over the years other than in minor refinements. Essentially, the equipment has a lathe-like configuration with two heads, at least one of which can be moved along the length of the machine to accommodate strings of varying length. Each head is provided with a fastening device, such as a hook, chuck, or other means to grip one end of the core wire. Each hook is arranged to rotate about its own central axis in a direction such that the core wire, when mounted on the hooks, will also rotate about its own lengthwise axis during the wrapping operation. Both hooks must rotate in phase at exactly the same number of revolutions per unit of time in order to avoid torsional twisting of the core wire. The hooks are normally driven by system of shafts and gears connected to a single drive motor. A force is provided, sometimes fixed, sometimes variable, for stretching the core wire in tension during the wrapping operation. Actuating means are provided for starting and stopping the rotation of the core wire, such actuating means usually being under the control of the machine operator. Means are also provided to flatten the core wire for a short distance at each end of the portion of the wire which is to receive the wrapping so that the ends of the wrapping wire may be anchored to the core wire, usually by swaging against the flattened portions of the wire so that the ends of the wrapping wire cannot turn relative to the core wire.
Historically, the application of the wrapping wire to the core wire has been done manually by the machine operator, usually by withdrawing the wrapping wire from a spool located near the machine and wrapping the free end around one of the flattened portions of the core wire, including the breaking-off of the leftover end of the wrapping wire, whereupon the machine is started to rotate the core wire. The operator feeds the wrapping wire onto the core wire by hand, the operator providing the necessary restraining tension on the wrapping wire and also maintaining the required angle between the axes of the core and wrapping wire during the wrapping operation. As the wrapping wire approaches its end point, the operator turns off the machine so as to brake it to a stop when the wrapping wire reaches the end of the other flattened portion of the core wire. As can be appreciated, such machines require a considerable amount of operator training and experience in order to produce usable strings, it being necessary for the operator to judge the correct pull and angle of the wrapping wire in order to produce a uniform and correct winding, and it is also necessary to judge when to turn-off the machine in order that the last turn of the wrapping wire will coincide with the end of the flattened portion of the core wire. With machines of this type, the production of strings of consistent musical quality is essentially an art depending upon the skill of a particular machine operator; and while the techniques of machine operation can be passed from operator to operator, there has been no known set of standards by which strings of consistent quality can be made by different operators, or even by the same operator at different times.
While various refinements have been added to the machines over the years to mechanically control portions of the winding operation, the machines are still basically manually controlled by the operator and subject to numerous variables and human error. For example, the wrapping wire supply spool has been mounted for movement along the length of the machine as the winding operation progresses, the spool being mounted on a carrier having a lead screw arrangement for moving the carriage in timed relation to the rotation of the core wire. An adjustment for wrapping wire tension is also provided on some machines, as by means of a friction-type brake which engages the wrapping wire. Variation in tension is achieved by tightening a set screw which increases or decreases the frictional drag exerted by the brake on the wrapping wire. Suffice to say, however, that such refinements are in themselves relatively crude and do not take into account many of the parameters which have been found essential to produce wrapped strings of uniformly high quality.
In contrast to the prior art equipment characterized above, the present invention provides a unique string wrapping machine which is essentially automatic in operation and effectively free from human error so that strings of uniformly high and consistent quality may be reliably produced.